The present invention relates to a method for preventing a metal material or steel plated with metal from the formation of white rust, a primary anticorrosion, and a pollution-free anticorrosive treatment as a primer coating without a chromate.
An anticorrosive treatment for zinc or aluminum plated steel sheet or non-plated steel has been researched and actually used for a long time. As conventional anticorrosive coatings chromate-based anticorrosive coatings are exemplified typically in Japanese Patent Application KOKAI No.131370/1991 in which anticorrosive coatings containing aqueous resins and chromate are disclosed. Such chromate-based anticorrosive coatings, however, are restricted in use because of the high toxicity and the carcinogenicity. In addition, the corrosion resistance is insufficient in some cases.
Alternatively, various kinds of chromium-free, so-called non-chromium type anticorrosive coatings have been developed recently. Non-chromium type anticorrosive coatings containing a compound having a carbodiimide bonding, an organo-silicate and silica particles are disclosed in Japanese Patent Application KOKAI No. 221595/1997, which relates to a multi-layer film, and is insufficient in the corrosion resistance as a single layer.
Generally, the non-chromium treatment using non-chromium type anticorrosive coatings has a problem that the adhesion after applying is not always sufficient. When a paint is applied on a chromate film, a strong adhesion is achieved between a chromate film and a topcoat paint film, as a chromium ion in the interface is used for the cross-linking of the paint resin in the chromate treatment. On the contrary, in the case of the non-chromium treatment, such a strong adhesion can be hardly attained.